This invention relates to a process for producing halogenated bis-imide flame retardant products having good color.
As is taught in U.S. Pat. No. 4,374,220, there are a multitude of halogenated bis-imides which are effective as flame retardants in composition with macromolecular flammable materials, e.g. polymers. These compositions are useful in making articles such as wire insulation and electronic housings. Of these halogenated bis-imides, the alkylene(C.sub.1 -C.sub.5)-bis-(tetrabromophthalimide)s are especially commercially significant.
A presently used commercial route for producing products predominant in alkylene(C.sub.1 -C.sub.5)-bis-(tetrabromophthalimide)s comprises reacting tetrabromophthalic anhydride with a diaminoalkane in the presence of water and an alkanoic acid to yield a reaction mass containing the intermediate, alkylene-diammonium-bis-(tetrabromophthalate). The reaction mass is then heated to about 210.degree. C. for a period of about 8 hours to yield the desired alkylene(C.sub.1 -C.sub.5)-bis-(tetrabromophthalimide) predominant product which is then recovered therefrom. This product is particularly useful as it has good thermal stability and resistance to UV degradation. However, the product has a yellow color which argues against its presence in compositions used for forming white articles. Also, the intensity of the yellow color can vary between product batches, which color variance makes it difficult for the article manufacturer to maintain consistency in the color of the articles produced.
It is therefore an object of this invention to provide a method for producing a white or at least near-white alkylene(C.sub.1 -C.sub.5)-bis-(tetrabromophthalimide) predominant product from a likewise predominant yellow product produced by the reaction of tetrabromophthalic anhydride and diaminoalkane in the presence of water and alkanoic acid.